Adjustable magnetic focusing system for beam tubes



Feb. 1, 1955 c, E, mcH 2,701,321

ADJUSTABLE MAGNETIC FOCUSING SYSTEM FOR BEAM TUBES Filed July 16, 1951 XNVENTOR GIL/ARLES E. fP/(JH ATTORNEY United States Patent ADJUSTABLE MAGNETIC FOCUSING SYSTEM FOR BEAM TUBES Charles E. Rich, Hempstead, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application July 16, 1951, Serial No. 236,903

14 Claims. (Cl. 313-84) The present invention relates to apparatus for producing specially distributed magnetic fields, and 1s part1cularly concerned with apparatus suitable for achieving a desired elongated magnetic field distribution for electron path control in electron beam tubes.

It is a principal object of this invention to provide such a magnetic path arrangement as will permit the production of a magnetic field substantially symmetrical about an axis along which it is directed, even where the field-inducing means is asymmetrical about the axis.

It is a further object of this invention to provide magnetic field apparatus wherein the magnetic field directed generally along the axis may be adjusted to an optimum distribution of flux lines about the axis.

Yet a further object is to provide, in an electron beam tube system wherein an intense magnetic field along the beam is employed for beam focussing, an arrangement enabling the magnetic field distribution to be modified conveniently and adjusted to the optimum field distribution relative to the required electron beam path, the system being mechanically stable whereby permanence of the optimum field distribution is reasonably assured.

Round magnetic pole pieces with central apertures have heretofore been used in beam tubes such as klystrons and travelling wave tubes, in connection with a permanent magnet of either bar or U-shape, the ends of the magnet being in direct contact with side areas of the pole pieces. Because of the asymmetry of the magnet about the electron beam axis, the magnetic field lines usually are found to be asymmetrically distributed about the axis. This asymmetry prevents the magnetic system from yielding the desired precise path control of the electron stream. Furthermore, the asymmetrically situated appurtenances of the electron beam tube, such as tuner elements and energy-coupling elements, usually cause objectionable effects on the magnetic field distribution between the pole pieces.

In accordance with the present invention, the foregoing objectives are met and the above disadvantages are substantially overcome by the introduction of a ring of highly permeable material between each end of the magnet element and the respective permeable pole piece, the ring being adjacent to the pole piece substantially throughout its circumference, but being spaced therefrom to provide a low-permeability gap therebetween, such as an air gap of unity permeability. Means are provided for adjusting the relative positions of the rings and the respective pole pieces, whereby the distribution of the magnetic field lines about the axis of the tube may be set for the optimum tube performance.

In the drawings, Fig. 1 is a side view, partly in section, of a preferred embodiment of the present invention, and

Fig. 2 is a partial crosssectional view taken on the line 22 in Fig. 1.

The tube system illustrated in Figs. 1 and 2 comprises an electron beam tube 11 and a magnet system 13 therefor. The electron beam tube 11 comprises an electron beamoriginating gun 15 which includes a cathode and at least one focussing electrode. The electron gun 15 is arranged to project an extremely compact pencil beam of electrons of very high current intensity, for travel at high velocity through a series of three cavity resonators 17, 19 and 21, situated along the axis of tube 11. That portion of the electron stream passing on through and beyond resonator 21 impinges upon collector element 23, in a specially shaped electron receiving cavity therein. A high electron accelerating potential is supplied, as by a rectifier power 2,701,321 Patented Feb. 1, 1955 ice supply, between the cathode of the tube 11 and the metallic body portions thereof, including wall 25, the cathode being negative and the body portions being positive, for accelerating the electrons in the beam to the high velocity for projection through the resonators, for the necessary power capability of the tube.

Drift tube portions 27 and 29 are provided within the reentrant portions of the resonators, wherein faster electrons overtake slower electrons to arrive at resonator 19 and resonator 21 in compact bunches, for medium power energization of the intermediate resonator 19 and for energization of resonator 21 at a very high microwave power level.

Means are provided for individual tuning of each of the three resonators 17, 19 and 21, to enable these resonators to be tuned to a desired operating frequency. The tuning unit for resonator 19 is illustrated as comprising a transversely adjustable piston 31 vacuum sealed to the cylindrical wall of the klystron through a bellows 33 and arranged to be adjusted to the desired tuning position by an adjusting screw 35. The tuning units for resonators 17 and 21 may be constructed in the same way as tuner 31, 33, 35, and may be situated at other angular orientations about the axis of the tube, for convenience and accessibility.

Microwave energy coupling means, not shown, are provided for introduction of energy into resonator 17, and for energy output coupling from resonator 21. A microwave energy coupler may also be included in resonator 19. The types of couplers employed will depend generally upon the system application of the tube, one example being coaxial connectors with coupling loops extending within resonators 17 and 19, and a wave guide output coupler having its inner end communicating with the interior of resonator 21. The features of transversely adjustable piston tuners and of input and output couplers of the wave guide type and the type including a coaxial line and a coupling loop are set forth in Patent No. 2,375,223 to W. W. Hansen et al., issued May 8, 1945.

The arrangement of the elements in electron gun 15 may be as illustrated in prior application Serial No. 117,187, filed September 22, 1949, now Patent No. 2,687,490 to C. E. Rich et al., issued August 24, 1954.

Pole pieces 41 and 43 having generally cylindrical exterior surfaces are included as part of the evacuated envelope for the electron beam tube 11, for use within a magnetic circuit wherein magnetic field lines are to be produced substantially parallel to the axis of the tube.

A permanent magnet unit 45, resembling a horseshoe magnet, is provided for inducing the magnetic flux lines between the faces of the pole pieces 41 and 43.

According to prior art constructions, the ends of the magnetic unit 45 would be joined directly to the outer surfaces of the respective pole-pieces 41 and 43. In accordance with the present invention, however, such direct contact between the magnet-ends and the pole-pieces is avoided; and instead, magnetic coupling rings 47 and 49 are arranged in direct contact with the magnet ends, the inner surfaces of these rings surrounding the outer surfaces of the respective pole pieces 41, 43 and being spaced therefrom and arranged for adjustable positioning with respect thereto. A set of three or more adjusting screws 51 may be provided in each of the rings 47, 49 to bear substantially radially against the adjacent pole piece. By manipulation of these screws 51, each soft iron magnetic coupling ring may be adjusted to a position concentric with the respective pole piece, or it may be adjusted to a position of eccentricity with respect thereto in any desired direction, and to any degree within an appreciable range of adjustment, as clearly illustrated in the sectional view of Fig. 2.

Magnetic coupling rings 47 and 49 are assembled into a rigid system in connection with the pole ends of magnet 45. Each of the rings 47 and 49 comprises two substantially semicircular pieces, which are arranged to be oined in a mortise joint and pinned together substantially opposite the region of the butt junction with the magnet 45. The two halves 55 and 57 of ring 47 are shown in Fig. 2, mortised together at 59, and meeting in a butt joint 61. Flat areas 63 and 65 are provided on the semicircular pieces 55 and 57, against which an end of magnet 45 rests in intimate contact. A rigid spacer member 67, constructed of non-magnetic material such as brass, is provided between the pole ends of the magnet 45. The rings 47 and 49 are attached as by screws to the flanged ends of the spacer 67. A pair of plates 69 and 71 are attached to the spacer 67, and are attached at 75 and 77 to the magnet system 45.

In order for the magnetic coupling rings 47 and 49 to be freely movable with respect to the pole pieces 41 and 43, by the adjustment of the screws 51, the entire magnet system 45 must be free to move along with the rings 47, 49. Since the mass of the magnetic system is appreciably greater than that of the beam tube itself, the overall assembly may be suspended by rigidly mounting the magnet system, the klystron beam tube then being held fixed in position by the screws 51 with respect to the magnet and the rings 47 and 49 which are rigidly fixed to the magnet.

In operation of the beam tube system, the screws 51 may first be set for substantially concentric positioning of the magnetic coupling rings 47 and 49 about their respective pole pieces 41 and 43. The cathode in the electron gun is heated, and the normal operating potential is supplied between the cathode, which is negative, and the body system which includes plate 25, pole pieces 41 and 43 and the metal elements which define cavity resonators 17, 19 and 21, which is positive.

Microwave input energy is supplied to resonator 17, and the output from resonator 21 is coupled to a high frequency energy load and high frequency energy indicating device, such as a microwave wattmeter. When the tuning units of the resonators 17, 19 and 21 have been adjusted to yield maximum output from resonator 21, the amount of output therefrom is noted. The substantially radial screws of each coupling ring are then readjusted, changing the spacing of each coupling ring from the position of substantial concentricity with its respective pole piece, first in one direction and then in another, until the directions and extents of displacement of the respective coupling rings for maximum performance have been attained. The positions of the coupling rings are not readily predeterminable, but instead, are found to require individual adjustment, according to the requirements of each individual tube and magnet combination.

Factors which are believed likely to require compensation through the adjustable positioning of the coupling rings 47 and 49 are the following:

(a) The tendency of the asymmetrically situated magnet system 45 to produce some curvature and lack of uniformity of distribution of the magnetic flux lines between the faces of pole pieces 41 and 43.

(11) Possible minute misalignments of the drift tubes 27 and 29 and the electron gun.

(c) The presence of materials such as ferrous alloys in the tuning units and in the input or output couplings, tending to cause some efiect upon the distribution of the magnetic flux lines.

(d) Partial saturation or non-uniform flux density in pole piece when magnet is placed directly in contact with one side of pole piece.

Yet other factors may be present which require compensation through the final adjustment of the positioning of the rings 47 and 49. In any event, it has been found that greatly improved tube performance is readily obtainable by the positional adjustment of the coupling rings, and that this system may be relied upon as a particularly convenient and stable means for obtaining the necessary magnetic field distribution in each tube to provide efficient operation thereof.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A magnetic field system comprising first and second pole pieces aligned along an axis, at least one of said pole pieces being apertured for permitting passage of an electron stream therethrough along said axis, first and second annular rings surrounding said respective pole pieces with an annular air gap between each ring and its surrounding pole piece, said pole pieces and said rings being made of highly permeable material, and means extending between said rings for inducing a strong magnetic field from one ring toward the other ring, at least one of said pole pieces being eccentrically situated with respect to its surrounding annular ring, the degree and direction of eccentricity being set to produce magnetic flux which is substantially symmetrical about said axis between said first and second pole pieces.

2. A magnetic field system for electron beam focussing, comprising first and second round pole pieces of highpermeability metal, said pole pieces being spaced an appreciable distance apart, a first ring of high-permeability metal adjacent to but spaced a finite distance from said first pole piece and a second ring of high-permeability metal adjacent to but spaced a finite distance from said second pole piece, at least one of said pole pieces being centrally apertured for permitting passage of an electron stream along an axis therethrough, and means including at least one magnetic element extending between said first ring and said second ring for providing a magnetic field between said first and second pole pieces, at least one of said pole pieces being eccentrically situated by a predetermined degree and direction with respect to its adjacent ring to produce magnetic fiux which is substantially symmetrical about said axis.

3. A magnetic field system comprising first and second centrally apertured round pole pieces of high-permeability metal, said pole pieces being spaced an appreciable distance apart along an axis with said apertures aligned concentrically with said axis, a first ring of highpermeability metal adjacent to but spaced a finite distance from said first pole piece and a second ring of highpermeability metal adjacent to but spaced at finite distance from said second pole piece, means coupled to said pole pieces for adjusting said pole pieces to different relative positions of eccentricity with respect to said rings, and means including at least one magnetic element extending between said first ring and said second ring for providing a magnetic field between said first and second pole pieces.

4. A magnetic field system as defined in claim 3 wherein each of said pole pieces has a substantially cylindrical outer surface, the respective rings having substantially cylindrical inner surfaces of greater diameter than the outside diameters of said pole pieces.

5. A magnetic field system as defined in claim 4 wherein said adjusting means comprise a plurality of screw struts threadedly installed in each of said rings and substantially radially extending therethrough to bear against the respective pole piece, said screw struts comprising means for adjustment of the positional relation between each ring and the respective pole piece, and for maintaining the relative positions thereof fixed after adjustment.

6. A magnetic field system comprising first and second pole pieces of higlrpermeability metal, at least one of said pole pieces including an aperture therein for passage of an electron beam along an axis therethrough, said pole pieces being spaced an a preciable distance apart, a first ring of high-permeability metal adjacent to but spaced a finite distance from said first pole piece and a second ring of hi h-permeability metal adiacent to but spaced a finite distance from said second pole piece, means between said rings and pole pieces for adjusting the relative positions of said rings and the respective pole pieces in planes transverse to said axis, and means coupled to said rings for inducing a magnetic field between said rings whereby a controllable field distribution is produced between said pole pieces.

7. An electron beam tube apparatus comprising first and second pole pieces of high-permeability metal, said pole pieces being spaced an appreciable distance apart along an axis of symmetry thereof, said first pole piece being centrally apertured, means for projecting a stream of electronsalong said axis through the aperture of said first pole piece toward said second pole piece, a first ring of high-permeability metal adjacent to but spaced a finite distance from said first pole piece and a second ring of high-permeability metal adjacent to but spaced a finite distance from said second pole piece, and means holding each at said first and second rings in a fixedly spaced position relative to said first and second pole pieces, said means being adjustable for maintaining said rings and respective pole pieces in an eccentric relationship.

3. Electron beam tube apparatus as defined in claim 7, further including means for producing a magnetic field extending between said first and second rings, whereby lines of magnetic force are induced between said pole pieces.

9. Electron beam tube apparatus as defined in claim 8, wherein said magnetic field producing means comprises a permanent magnetic element coupled between said first and second rings.

10. Electron beam tube apparatus as defined in claim 7, wherein said first and second pole pieces have substantially cylindrical outer surfaces, and said first and second rings have substantially cylindrical inner surfaces of greater diameters than the respective outer diameters of said cylindrical surfaces of said pole pieces.

11. Electron beam tube apparatus as defined in claim 7, wherein said first and second pole pieces have substantially cylindrical outer surfaces, and said first and second rings have substantially cylindrical inner surfaces of greater diameters than the respective outer diameters of said cylindrical surfaces of said pole pieces, said adjustable means holding said rings and said respective pole pieces in fixed positional relation comprising a plurality of radially disposed screw struts in each of said rings for bearing against the respective pole pieces, said screw struts comprising means for adjusting the positional relations of the respective rings and pole pieces for optimum electron beam control.

12. Electron beam tube apparatus as defined in claim 7, wherein said first and second pole pieces have substantially cylindrical outer surfaces, and said first and second rings have substantially cylindrical inner surfaces of greater diameters than the respective outer diameters of said cylindrical surfaces of said pole pieces, said means for holding said rings and said respective pole pieces in fixed positional relation comprising a plurality of radially disposed screw struts in each of said rings for bearing against the respective pole pieces, said screw struts comprising means for adjusting the positional relations of the respective rings and pole pieces for optimum electron beam control, said electron beam tube apparatus further including means for producing an intense unidirectional magnetic field between said first and second rings whereby a magnetic field is provided, generally along said axis between said first and second pole pieces.

13. An electron beam tube apparatus, comprising an evacuated envelope including first and second pole pieces of high-permeability metal, said pole pieces being spaced an appreciable distance apart along an axis of symmetry thereof, said first pole piece being centrally apertured, means for projecting a stream of electrons along said axis through the aperture of said first pole piece toward said second pole piece, a first ring of high-permeability metal adjacent to but spaced a finite distance from said first pole piece and a second ring of high-permeability metal adjacent to but spaced a finite distance from said second pole piece, said first and second rings being external of said evacuated envelope, and means holding said first and second rings fixedly spaced relative to said first and second pole pieces.

14. An electron beam tube apparatus comprising first and second pole pieces of high-permeability material, said pole pieces being spaced an appreciable distance apart along an axis of symmetry thereof, said first pole piece being centrally apertured, means aligned with said axis for projecting a stream of electrons along said axis through the aperture of said first pole piece toward said second pole piece, a ring of high-permeability metal adjacent to but spaced from one of said pole pieces, means for inducing a polarized field between said one pole piece and the other of said pole pieces generally along said axis, said inducing means being coupled to said ring, and means coupled to said ring for adjusting the positional relation between said ring and the pole piece adjacent thereto in a plane transverse to said axis for selectively modifying the magnetic field distribution between said pole pieces.

References Cited in the file of this patent UNITED STATES PATENTS 2,157,182 Maloff May 9, 1939 2,188,579 Schlesinger Ian. 30, 1940 2,193,602 Penney Mar. 12, 1940 2,200,039 Nicoll May 7, 1940 2,305,884 Litton Dec. 22, 1942 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr. 8, 1947 2,455,676 Hillier Dec. 7, 1948 2,533,687 Quam Dec. 12, 1950 

